The study seeks an understanding in detail of the kinetic, chemical, and complete metal ion dependent stereochemical mechanisms utilized by the first enzyme of histidine biosynthesis in Salmonella typhimurium, ATP phosphoribosyltransferase (EC 2.4.2.17). Characterization of the binding order of the substrates ATP and phosphoribosylpyrophosphate to the enzyme is sought using isotope exchange at equilibrium, and equilibrium binding experiments. Localization of the guanosine tetraphosphate binding site on the enzyme is sought using kinetic and equilibrium substrate competition approaches. Conformational changes in the enzyme induced by ATP and by the inhibitors, ADP, AMP and guanosine tetraphosphate would be characterized with difference spectroscopy and temperature jump techniques. Exchange inert CoIII complexes of the substrates and of ADP and guanosine tetraphosphate would be synthesized and used for conformation and rate studies similar to those above. Metal ion stereochemical requirements for substrates and inhibitors would be determined using CoIII complexes. The regions of the enzyme polypeptide forming the active site would be determined by covalent affinity labeling. The long term goal is to understand mechanistically how integrated metabolic regulation by the general amino acid pool and energy charge is effected in amino acid biosynthesis.